Electrical arc welding



tatev assignor to Hartford. National Bank and Trust Company, Hartford, Comm, as trustee No Drawingw Application November'7, 1951, Serial'No. 255,331

In N ether-lands July 25, 1944 Section 1, Public-Law69fi,August 8,1946 Patent expires July 25, 1964 l-Claimt chin-40o This application is adivision of-my co-pending U. S. application Ser. No. 641,628, filed January 16, 1946, now abandoned.

It is knownto provide certain contrivances at the end of coated Welding electrodesfor readily starting the welding arc. Thus, for example, it was suggested before to provide the bare ground end of the weldingelectrode with a small conductive hood which constitutes a short-circuit bridge. In addition, a welding electrode has been described whose core'for this purposeends in a coated tip. Such welding electrodes "with'which rapping of the piece of work for starting the arc can be omitted, may be designated as self-starting welding electrodes. A disadvantage of these Well-known welding electrodes consists in that on interruptionof-the welding operation or on extinction of=the arc, which is .liable to occur when using certain coating ingredientscr a lowno-load voltage of the weldingapparatus, the .welding arc cannot be re-started without additional means it beingagain necessary to resort to the 'normalarc-starting manner.- This is particularly inconvehient in the use of touch-Welding electrodes.

The inventionhas for one. of its objects to avoid the difficulties. involved by. the. use ofath'e above-mentioned well-known self-starting welding-rods. or electrodes in touch-welding; as is well-known the coating of the welding electrodes iskept incontiiiu'ou's contact with the piece of work in this method.

The invention is based on recognition of the fact that this can be ensured by rendering the coating throughout its length electrically conductive to a certain extent. In addition, the coating should be enabled by its thickness to constitute such a deep cup that short-circuit of the core of the Welding rod with the piece of Work is avoided.

It is a further object of the invention to provide the core of a Welding electrode with such a coating that in touchwelding the arc is started and restarted by contact of the coating at the Welding end of the electrode with the workpiece.

On an electrode of the type which has a coating con taining a large proportion of metal powder an arc is started when an electrical current of substantial magni tude passes through the coating.

Thus an electrode is only selfstarting if the coating thereon is conductive. It has been found that this conductivity requirement of the coating is met, if sparking occurs distinctly, when at an applied voltage which is equal to the no-load voltage to be used in the welding apparatus, the coating of the welding electrode is brushed in the direction of its length along an edge of a conductive body included with it in a circuit. An ammeter connected in this case into the circuit registers a constantly fluctuating deflection. The mean value of the current passing through the coating may be estimated during this observation. At a voltage of about 50 volts, for example,

this current, expressed in milliamperes, is found to have a value of at least the order of magnitude of 10 The greater the conductivity of the weldingelectrode coating, 1

the more readily the welding arc'will start;-

It has also been found, however, that a touchwelding electrode with a conductivefcoating, for example a coating containing a large percentage of metal powder is likely to show an une've'n burningandfreezing onto the workpiece.

Uneven burning is here understood to mean the forma-.

oi -the crater. tance' ofthe core end -of' the 'elect'rode "to the workpiece and thus in shortening the aro length until the arcv isshort circuited by molten' met'al. Then the'arc extinguishes' and the metal solidifies thereby securing the weldinglelectrode on the workpiece which-phenomenon is here desig-:

nated' as freezing? Ithas been found thatthese'phenomena result from a=comparatively high electric current which" traverses "the' co'ating during welding and that touchwel'ding- 'can only be perfo'rmed without occurrence of these'phenomena if thecoating acts asan insulator.

A further accurate study of these phenomena showed however that an electric current of low magnitude "does not necessarily bring about the disadvantages in touch welding described above and also that thiscurrent is sometimes sufiicient to allowthe arc to be ignited by simply contacting the workpiece with the coated welding end the'electrodei The welding electrode'accordingto'the present invention is characterized-in that'at normal no-load voltage, the coating of-whichcontains metal powder, passes a current capable of initiating the welding arconcontact of the coating with the workpiece but which current is so low that it is notcapable of'bringing' about'thephenomenaof uneven' burning and f're'ezin'g.

in view of the easy re-starting of'thewelding arc, the invention isparticullarl'y important when using a coating which for metallurgic reasons contains 1 substances having the "disagreeable property 'ofassisting extinction "of the are. Such is the case for example-'when using 'onabase coatings of fluoride and alkaline earth carbonate with core wire substantially constituted by iron. This ensures welds having very satisfactory mechanical properties, more particularly having a high impact value.

As an example of a welding electrode composed according to the invention I covered a mild steel core having a diameter of 4 mm. by extrusion with a mixture composed of 16% of calcium fluoride 16% of calcium carbonate 6% of ferro-titaniun1+ferro-silicon+ferro-manganese 54% of pulverulent iron 8% or" water glass and aluminum silicate up to a diameter of 8.5 mm.

In addition the invention is particularly important in connection with Welding by means of Welding electrodes having a core or" larger diameter than usual, that is to say, having a core of over 6 mm., for example 10 mm. Welding by means of heavy welding electrodes of this kind generally involves serious dilficulty, such as fatigue of the welder by the large weight of the welding electrode, intense thermal radiation due to the high welding current and troublesome spraying of the Welding metal. in touchwelding according to the invention this difiiculty is largely obviated, since both during starting of the arc and during the subsequent welding the electrode rests on the piece of work so that the weight is not a source of trouble,

Patented; Jam; 10, 71956 and in addition the thermal radiation and the spraying are limited by the deep cup constituted by the coating during welding.

Furthermore the welding electrode according to the invention is characterized in that it is at least twice as thick as the metal core so as to enable the electrode to be used in touchwelding.

To satisfy the conductivity requirements mentioned above the metal content of the coating should have a value of between 50 and 65% by weight. It has been found that the short range of metal contents of the coating which brings about the conductivity requirements of a welding electrode according to the invention generally falls within this range of from 50 to 65 of the weight of the coating and that whether this range is near the lower or near the higher value or covers intermediate values depends on characteristics of the coating such as the proportion and nature of the other coating ingredients.

The invention thus comprises a welding electrode being composed of a core and a coating, the thickness of the electrode being at least twice the thickness of the core and the coating containing metal powder within the range of from 50 to 65 by weight, so that upon normal no load voltage the coating passes a current capable of initiating the welding are on contact of the coating with the workpiece but which current is so low that it is not capable of bringing about the phenomena of uneven burning and freezing in touchwelding. Welding electrodes which have a coating comprising metal powder have been described but the welding electrodes according to the invention are difierentiated therefrom because they have an unusual thick coating and because they have to comply with the conductivity requirement of the coatings specified above.

Similar to normal welding electrodes the welding electrodes according to the invention may be coated simply by extrusion so that their manufacture is easier than that of the well-known, above-mentioned self-starting welding electrodes at whose welding end special initiating devices are provided.

According to the invention, a satisfactory weld may be secured without any trouble for example by means of a welding electrode whose core of mild steel has a diameter of 10 mms. and which is coated up to a thickness of 22 mms. with material containing a large quantity of the welding metal in a divided form. This material may be made up for example of:

4f 12% of calcium fluoride 13% of calcium carbonate 7% of ferrous alloys 61% of pulverulent iron 7% of water glass and aluminum silicate.

According to the invention,'such a welding electrode allows of welding with a current of about 1200 amp. without any need of taking particular precautions for protecting the welder. In contradistinction to this, welding by means of a welding electrode of identical total composition having all of the welding metal contained in the core is no longer feasible at an identical welding current.

While I have shown and described the preferred embodiment of my invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claim.

What I claim is:

A welding electrode comprising a metal core having a diameter of 10 mms., a slag-forming conductive coating for said electrode comprising a mixture of 12% of calcium fluoride, 13% of calcium carbonate, 7% of ferrous alloys, 61% of pulverulent iron, and 7% of water glass and aluminum silicate, the thickness of the electrode being at least twice the diameter of the core whereby at no-load voltage of the welding apparatus the coating passes a current capable of initiating a welding are on contact of the coating with a work piece.

References Cited in the file of this patent UNITED STATES PATENTS 1,294,250 Elliott Feb. 11, 1919 1,329,530 Kinhead Feb. 3, 1920 1,898,908 Southgate Feb. 21, 1933 2,009,240 Roberts et a1 July 23, 1935 2,146,600 Somerville Feb. 7, 1939 2,394,550 Jensen Feb. 12, 1946 2,408,620 Friedlander Oct. 1, 1946 2,429,175 Willigen Oct. 14, 1947 FOREIGN PATENTS 553,371 Great Britain May 19, 1943 

